1. Field of the Invention
The present invention relates to a machine for printing on articles that are substantially in the form of bodies of revolution.
2. Description of the Related Art
A printing machine of this type includes a turntable carrying mandrels on which the articles for printing are engaged, and a plurality of printer stations for printing different colors that are arranged beside one another around the turntable.
The turntable is adapted to move the articles from one printer station to another. The position of the article for printing is identified in an identification station. Thereafter, the article is moved by the turntable to face a first printer station suitable for projecting ink of one color onto the article in order to print a portion of the pattern for printing in said color. Thereafter, the article is moved by the turntable towards a second printer station suitable for projecting ink of another color in order to print another portion of the pattern for printing.
When a pattern for printing has two different colors juxtaposed, it is necessary for a portion of the pattern of one color not to be printed on a portion of the pattern of another color. Similarly, the portions that are of different colors must all be printed beside one another without any non-printed spaces appearing between them.
Nevertheless, it is difficult to guarantee the position of the article-carrier mandrel relative to the printer station, since it is not possible mechanically to displace the turntable from one printer station to another with great accuracy.
In addition, since each of the printer stations is directed towards the center of the turntable, the triggering of ink projection from each printer station must take account of the angle defined by each of the printer stations relative to the center of the turntable, because the orientation of the article is modified by said angle on going from one printer station to another.
Consequently, it is difficult to satisfy the accuracy requirements of the manufacturers of articles when using a printing machine of that type.
U.S. Pat. No. 6,135,654 describes printing apparatus having a conveyor for conveying articles and three print heads disposed facing the part along which the conveyor brings the articles. The articles are placed on guides suitable for rotating the articles about their axes of symmetry.
Nevertheless, the rotary drive applied to the articles is not accurate, and as a result the colors are sometimes offset relative to one another.
Document FR 2 755 900 describes a machine for printing strips of fabric at varying speeds. The machine is suitable for compensating deformation in the fabric. It has a fabric drive motor, print heads facing the fabric, a position encoder placed on the drive motor, a printing device arranged upstream from the print heads and suitable for printing marks on the fabric, and an optical system for reading the marks. The print heads are suitable for triggering printing on the fabric as a function of a signal delivered by the position encoder and as a function of the signal generated by the optical system.